Tubular oil filled electric bushing with sealing means

ABSTRACT

An oil filled electric bushing consists of an elongated, tubular insulator, through which an electric conductor extends. The conductor is provided at one of its ends with a terminal assembly comprising an inner tap firmly joined to the conductor and an external terminal tap threaded on to the inner tap and pressed against an end seal member. A resilient tubular locking pin holds the inner tap in a fixed position in relation to the end seal member.

United States Patent Sven Linderholm lnventor Ludvika, Sweden Appl. No. 32,114 Filed Apr. 27, 1970 Patented Oct, 5,1971 Assignee Allmanna Svenslta Elektriska Aktiebolaget Vasteras, Sweden Priority Apr. 30, 1969 Sweden 622/69 TUBULAR OIL FILLED ELECTRIC BUSHING WITH SEALING MEANS 4 Claims, 3 Drawing Figs.

US. Cl 174/75 R, 85/8.3,151/38,174/19, 174/77 R Int. Cl H02g 15/04,

[50] Field of Search 174/19, 31

' R, 74 R, 75 R, 75 D, 75 F, 80, 142, 143, 152 R, 167; 151/6, 38; 85/8.3

[56] Reierences Cited UNITED STATES PATENTS 1,691,328 11/1928 Austin 174/75 R 1,728,952 9/1929 Austin.... 174/75 R 2,109,368 2/1938 Eby 174/75 F X Primary Examiner-Laramie E. Askin Attorney-Jennings Bailey, Jr.

ABSTRACT: An oil filled electric bushing consists of an elongated, tubular insulator, through which an electric conductor extends. The conductor is provided at one of its ends with a terminal assembly comprising an inner tap firmly joined to the conductor and an external tenninal tap threaded on to the inner tap and pressed against an end seal member. A resilient tubular locking pin holds the inner tap in a fixed position in relation to the end seal member.

PATENTEDn cT 5m: 3510.813

JNVENTOR. SVEN UNDER HOLM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric bushing comprising an elongated tubular insulator provided with an end seal member and having a centrally located electric conductor extending through said insulator. The electrical conductor is provided at one of its ends with a terminal assembly comprising an inner connection tap and an outer terminal tap. The connection tap is firmly connected to the conductor and provided with an external screw thread, whereas the terminal tap is provided with an internal screw thread and threaded on to said connection tap so that it is axially pressed against said end seal member. A locking member is arranged to hold the inner connection tap in a fixed position in relation to the end seal member. Connection of outer conductors to the terminal tap can be made, for instance through a terminal plate, which is attached to the terminal tap by means of clamp members, suitable for this purpose.

2. The Prior Art Bushings with connection assemblies of said type are used to a great extent, for instance for transformers, and, generally, they work satisfactorily during normal operating conditions. When,-- however, the connection assembly is subjected to variations of temperature, vibrations or torque, transmitted from the outer conductor, there is a risk that the screw joint between the inner and outer tap may loosen, resulting in the disappearance of the contact force between the taps. This may result in abnormal heating of the connection assembly, and in certain cases disturbances in the normal operation may occur.

SUMMARY OF THE INVENTION The purpose of the invention is to obtain an effective locking of the screw joint between the two taps in the connection assembly so that the previously mentioned risks of disturbances are eliminated. The locking should be such that it prevents turning of, or makes it difficult to turn, the terminal tap. Furthermore, a satisfactory electric contact should be obtained even during initial turning.

According to the invention, this is achieved by making the locking member, which normally is used to hold the inner connection tap in a fixed position in relation to the end seal member, resilient in the longitudinal direction of the terminal tap. By using such a locking member the problem can be solved in a very simple way without simultaneously having to increase the number of construction elements in the connection assembly and without any great cost for reconstruction. Besides filling its earlier task, that is, to lock the inner tap in relation to the end seal, the resilient locking member will also exert a resilient force when the outer terminal tap is threaded on to the inner connection tap. This resilient force locks the screw joint and gives the necessary contact force at varying temperatures and under vibrations, even in the case of the terminal tap being subjected to a certain torque tending to loosen the screw joint.

For bushings of this type, it is usual to place the conductor in a bushing tube made of, for instance, aluminum, and arranged inside the tubular insulator. Thus, the inner connection tap usually is locked to the bushing tube with the aid of a cylindrical locking pin, arranged in a radial hole through the tube and the connection tap, which is inserted in the end of the tube. It has proved to be very suitable to make this locking pin of two resilient tube pins of the known type having a longitudinal slit, one pin being pressed into the other so that the slits are turned in opposite directions. The resilient properties of such a pin are the same in different radial directions, and it is not necessary to take any special measures to obtain a certain position of the slits of the tube pins.

. 2 BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS The condenser bushing shown in FIG. 1 consists of an elongated tubular insulating member 1 with an inner bushing tube 2, made of aluminum, through which a conductor 3 extends. The end of the bushing is provided with a connection assembly consisting of an inner tap 4 (called the connection tap) with an outer screw thread, and an outer tap 5 (called the terminal tap) with an inner screw thread. The inner top 4 is finnly connected with the conductor 3, for instance through brazing or contact pressing. Further, the inner tap 4 is locked to the bushing tube 2 by means of a resilient locking pin 6. For connection of outer conductors to the bushing a terminal plate, not shown, is attached to a terminal tap 5. When the terminal tap 5 is threaded on to the connection tap 4, it is pressed against an end seal member consisting of a nut 7 and a flange 8. Because of the resilient locking pin 6, a resilient force is obtained simultaneously, resulting in an efiective locking of the screw joint between the inner tap 4 and the outer tap 5. In addition to this, the locking pin maintains the contact force even in the case where the outer tap is subjected to a certain torque tending to loosen the screw joint. Test under working conditions have shown that the connection has considerably better properties in this respect than corresponding previously known embodiments in which a cylindric, nonresilient, locking pin was used. The bushing is filled with oil and, there fore, a seal 9 in the form of a so-called O-ring is arranged between the terminal tap 5 and the nut 7.

FIGS. 2 and 3 show how the resilient locking pin 6 is constructed. It consists of two resilient tube pins 10 and ll of different diameters, the smaller pin 10 being pressed into the bigger one so that the slits l2 and 13 of the pins are displaced in relation to each other.

The invention isnot limited to the embodiment shown. Thus, for instance, the resilient locking member can be constructed in several different ways within the scope of the invention. It would be possible, for instance, to use one single resilient tube pin, provided this has suitably resilient properties, instead of using two tube pins. In such a case it could be desirable to have a certain direction of the slits of the resilient pin. This can easily be made by means of a guiding pin, which is placed in a preferably radial hole in the connection tap, thus engaging with the slit, so that the tube pin comes to a fixed position. Further, the end seal member can be constructed in many different ways. For instance, it can be provided with a resilient member in order to maintain the necessary sealing pressure at different temperatures of the bushing.

Iclaim:

1. An electric bushing comprising an elongated tubular insulating member (1), said insulating member being provided with an end seal member (7,8), a centrally located electrical conductor (3) extending through said insulating member, said electrical conductor at one of its ends being provided with a terminal assembly comprising an inner connection member (4), said connection member being firmly connected to said conductor (3) and provided with an external screw thread; an outer terminal member (5) provided with an internal screw thread and threaded on to said connection member (4), the terminal member (5) being axially pressed against said end seal member (7,8), a locking member (6) holding said inner connection member (4) in a fixed position in relation to said end seal member (7,8), said locking member (6) being resilient in the longitudinal direction of said connection member (4), whereby to cause said outer terminal member to press against said seal member. v

3 4 2. A bushingaccording to claim 1,in whichametal tube (2) 4. A bushing according-.toclaim 1', in which said locking Surrounds Said connection member and is arranged in a member (6) comprises two concentric resilient tubular pins fixed position in relation to said end seal member (73) said (10,11), each provided with a longitudinal slit (12,13), one of locking member (6) comprising a pin arranged in radial holes v I said pins (10) being pressedmtothe other pin (11) with said through said connection member (4) and said metal tube (2). sms (12.13) turned in op itedirections.

3. A bushing according to claim 2, in which said pin (6) is a resilient tubular pin having a longitudinal slit. 

1. An electric bushing comprising an elongated tubular insulating member (1), said insulating member being provided with an end seal member (7,8), a centrally located electrical conductor (3) extending through said insulating member, said electrical conductor at one of its ends being provided with a terminal assembly comprising an inner connection member (4), said connection member being firmly connected to said conductor (3) and provided with an external screw thread; an outer terminal member (5) provided with an internal screw thread and threaded on to said connection member (4), the terminal member (5) being axially pressed against said end seal member (7,8), a locking member (6) holding said inner connection member (4) in a fixed position in relation to said end seal member (7,8), said locking member (6) being resilient in the longitudinal direction of said connection member (4), whereby to cause said outer terminal member to press against said seal member.
 2. A bushing according to claim 1, in which a metal tube (2) surrounds said connection member (4) and is arranged in a fixed position in relation to said end seal member (7,8), said locking member (6) comprising a pin arranged in radial holes through said connection member (4) and said metal tube (2).
 3. A bushing according to claim 2, in which said pin (6) is a resilient tubular pin having a longitudinal slit.
 4. A bushing according to claim 1, in which said locking member (6) comprises two concentric resilient tubular pins (10,11), each provided with a longitudinal slit (12,13), one of said pins (10) being pressed into the other pin (11) with said slits (12,13) turned in opposite directions. 